Question

我是android编程的新手。我想弄清楚如何使用this

中的代码

ContentResolver contentResolver = getContentResolver();
Uri uri = android.provider.MediaStore.Audio.Media.EXTERNAL_CONTENT_URI;
Cursor cursor = contentResolver.query(uri, null, null, null, null);
if (cursor == null) {
    // query failed, handle error.
} else if (!cursor.moveToFirst()) {
    // no media on the device
} else {
    int titleColumn = cursor.getColumnIndex(android.provider.MediaStore.Audio.Media.TITLE);
    int idColumn = cursor.getColumnIndex(android.provider.MediaStore.Audio.Media._ID);
    do {
       long thisId = cursor.getLong(idColumn);
       String thisTitle = cursor.getString(titleColumn);
       // ...process entry...
    } while (cursor.moveToNext());
}

我不知道如何处理条目或如何处理他们提供的其他代码块。

long id = /* retrieve it from somewhere */;
Uri contentUri = ContentUris.withAppendedId(
        android.provider.MediaStore.Audio.Media.EXTERNAL_CONTENT_URI, id);

mMediaPlayer = new MediaPlayer();
mMediaPlayer.setAudioStreamType(AudioManager.STREAM_MUSIC);
mMediaPlayer.setDataSource(getApplicationContext(), contentUri);

// ...prepare and start...

有人可以告诉我它是如何工作的以及如何检索数据。

Answer 1

我迟到但希望它会帮助你here是如何使用内容提供商使用内容提供商检索数据的一个很好的例子

import android.content.ContentResolver;
import android.content.ContentUris;
import android.database.Cursor;
import android.net.Uri;
import android.provider.MediaStore;
import android.util.Log;
import java.util.ArrayList;
import java.util.List;
import java.util.Random;

public class MusicRetriever {
final String TAG = "MusicRetriever";
ContentResolver mContentResolver;
// the items (songs) we have queried
List<Item> mItems = new ArrayList<Item>();
Random mRandom = new Random();
public MusicRetriever(ContentResolver cr) {
    mContentResolver = cr;
}
/**
 * Loads music data. This method may take long, so be sure to call it asynchronously without
 * blocking the main thread.
 */
public void prepare() {
    Uri uri = android.provider.MediaStore.Audio.Media.EXTERNAL_CONTENT_URI;
    Log.i(TAG, "Querying media...");
    Log.i(TAG, "URI: " + uri.toString());
    // Perform a query on the content resolver. The URI we're passing specifies that we
    // want to query for all audio media on external storage (e.g. SD card)
    Cursor cur = mContentResolver.query(uri, null,
            MediaStore.Audio.Media.IS_MUSIC + " = 1", null, null);
    Log.i(TAG, "Query finished. " + (cur == null ? "Returned NULL." : "Returned a cursor."));
    if (cur == null) {
        // Query failed...
        Log.e(TAG, "Failed to retrieve music: cursor is null :-(");
        return;
    }
    if (!cur.moveToFirst()) {
        // Nothing to query. There is no music on the device. How boring.
        Log.e(TAG, "Failed to move cursor to first row (no query results).");
        return;
    }
    Log.i(TAG, "Listing...");
    // retrieve the indices of the columns where the ID, title, etc. of the song are
    int artistColumn = cur.getColumnIndex(MediaStore.Audio.Media.ARTIST);
    int titleColumn = cur.getColumnIndex(MediaStore.Audio.Media.TITLE);
    int albumColumn = cur.getColumnIndex(MediaStore.Audio.Media.ALBUM);
    int durationColumn = cur.getColumnIndex(MediaStore.Audio.Media.DURATION);
    int idColumn = cur.getColumnIndex(MediaStore.Audio.Media._ID);
    Log.i(TAG, "Title column index: " + String.valueOf(titleColumn));
    Log.i(TAG, "ID column index: " + String.valueOf(titleColumn));
    // add each song to mItems
    do {
        Log.i(TAG, "ID: " + cur.getString(idColumn) + " Title: " + cur.getString(titleColumn));
        mItems.add(new Item(
                cur.getLong(idColumn),
                cur.getString(artistColumn),
                cur.getString(titleColumn),
                cur.getString(albumColumn),
                cur.getLong(durationColumn)));
    } while (cur.moveToNext());
    Log.i(TAG, "Done querying media. MusicRetriever is ready.");
}
public ContentResolver getContentResolver() {
    return mContentResolver;
}
/** Returns a random Item. If there are no items available, returns null. */
public Item getRandomItem() {
    if (mItems.size() <= 0) return null;
    return mItems.get(mRandom.nextInt(mItems.size()));
}
public static class Item {
    long id;
    String artist;
    String title;
    String album;
    long duration;
    public Item(long id, String artist, String title, String album, long duration) {
        this.id = id;
        this.artist = artist;
        this.title = title;
        this.album = album;
        this.duration = duration;
    }
    public long getId() {
        return id;
    }
    public String getArtist() {
        return artist;
    }
    public String getTitle() {
        return title;
    }
    public String getAlbum() {
        return album;
    }
    public long getDuration() {
        return duration;
    }
    public Uri getURI() {
        return ContentUris.withAppendedId(
                android.provider.MediaStore.Audio.Media.EXTERNAL_CONTENT_URI, id);
    }
}

希望这会对你有所帮助

从内容解析器中检索媒体

1 个答案: